Nine minutes later at 9:57 p.m. CDT, he was pronounced dead.
The state carried out the execution after the U.S. Supreme Court rejected his request for a reprieve in a split vote. Medellin, 33, claimed he was denied treaty-guaranteed help from the Mexican consulate when he was arrested. The court's deliberations delayed the lethal injection nearly four hours.
His execution, the fifth this year in the nation's busiest capital punishment state, attracted international attention because of the claims although Texas authorities said he never invoked his consular rights until four years after he was arrested. By then, he had been convicted and condemned of participating in the gang rape, beating and strangling of Elizabeth Pena, 16, and Jennifer Ertman, 14.
Pena's father, who was among the witnesses, gently tapped the glass that separated him from Medellin as he turned to leave the witness chamber after the execution.
"We feel relieved," Adolfo Pena said after leaving the prison. "Fifteen years is a long time coming."
Several dozen demonstrators, about evenly divided between favoring and opposing capital punishment, stood outside on opposite sides of the Texas Department of Criminal Justice Huntsville Unit, where executions are carried out. A driving rain, the remnants of Tropical Storm Eduardo, drenched many of them late Tuesday afternoon.
Sandra Babcock, one of Medellin's lawyers, while acknowledging an "unspeakable crime he committed many years ago," said her thoughts were with his family and the family of his victims and hoped they could find peace.
"Under the circumstances, it's hard to talk about what comes next," she said. "But now more than ever, it's important to recall this is a case not just about one Mexican national on death row in Texas. It's also about ordinary Americans who count on the protection of the consulate when they travel abroad to strange lands. It's about the reputation of the United States as a nation that adheres to the rule of law."
In Nuevo Laredo, Mexico, where Medellin was born, a small group of his relatives condemned his execution.
"Only God has the right to take a life," said Medellin's cousin Reyna Armendariz.
Six of his relatives, including Armendariz, and several activists gathered Tuesday in a working class neighborhood to await news on Medellin's fate.
A large black bow and a banner that read "No to the death penalty ... may God forgive you," hung from an iron fence in the front of the house where Medellin lived until moving to the United States at the age of 3.
Medellin, who grew up in Houston, and five fellow gang members attacked the two teenage girls as they were walking home on a June night in 1993, raped and tortured them for an hour, then kicked and stomped them before using a belt and shoelaces to strangle them.
Their remains were found four days later. By then, Medellin already had bragged to friends about the killings.
Medellin's lawyers asked the U.S. Supreme Court to stop the execution until legislation can be passed to formalize case reviews ordered by the International Court of Justice, a panel based in The Hague and also known as the World Court.
The court said in its ruling that those possibilities were too remote to justify a stay. Four justices issued dissenting opinions. Justice Stephen Breyer wrote that to permit the execution would place the United States "irremediably in violation of international law and breaks our treaty promises."
Gov. Rick Perry, Texas courts and the Texas attorney general's office all said the execution should go forward and that Medellin has had multiple legal reviews. State officials noted Medellin never invoked his Mexican consular rights under the Vienna Convention until some four years after he was convicted of capital murder.
The International Court of Justice has said Medellin and some 50 other Mexicans on death rows around the nation should have new hearings in U.S. courts to determine whether the 1963 treaty was violated during their arrests. Medellin is the first among them set to die.
President Bush asked states to review the cases, but the Supreme Court ruled earlier this year neither the president nor the international court can force Texas to wait. Medellin's supporters say either Congress or the Texas Legislature should be given a chance to pass a law setting up procedures for new hearings before he should be executed and that executing Medellin now would endanger Americans abroad.
"Flouting the World Court ruling would be yet another blight on America's already tarnished international reputation," said Sue Gunawardena-Vaughn, director of Amnesty International USA's death penalty abolition campaign. The human rights organization is opposed to capital punishment in all instances.
A bill to implement the international court's ruling wasn't introduced in Congress until last month and quick passage is considered unlikely. The Texas Legislature doesn't meet until January.
Randy Ertman, who lost his daughter in the attack, said Medellin's supporters were misguided.
"Mexico has a big yard down there full of filth and murders and gangs and drug cartels and they're not mentioning anything about that," he said. "There's where they need to start their work."
On Monday, the 5th U.S. Circuit Court of Appeals rejected a request for a reprieve and denied his lawyers permission to file new appeals. The Texas Board of Pardons and Paroles also rejected requests for clemency and a 240-day reprieve.
"I don't want sympathy or pity, I'd rather have your anger," Medellin said on an anti-death penalty Web site where prisoners seek pen pals. "Don't feel sorry for me. I'm where I'm at because I made an adolescent choice. That's it!"
He said he'd "grown up behind bars and if the state gets its wish I'll die behind a locked steel door."
He added, erroneously, "There's no bars in the death chamber."
One of Medellin's fellow gang members, Derrick O'Brien, was executed two years ago. Another, Peter Cantu, described as the ringleader of the group, is on death row. He does not have a death date.
Two others, Efrain Perez and Raul Villarreal, had their death sentences commuted to life in prison when the Supreme Court barred executions for those who were 17 at the time of their crimes.
The sixth person convicted, Medellin's brother, Vernancio, was 14 at the time and is serving a 40-year prison term.
Mark Vinson, the Harris County assistant district attorney who prosecuted Medellin and is now retired, said it was interesting to him that none of the prisoner's appeals focused on his guilt or the evidence.
"I just think under cloak and dagger they're trying to reach out and grab something," he said. "I believe instead of playing this game, he should reach out to his creator. He needs to spend his time praying to his creator for mercy and forgiveness."
At least six other Mexican nationals have been executed in Texas since 1982.
On Thursday, a Honduran man, Heliberto Chi, 29, is set to die for the slaying of a suburban Dallas clothing store manager during the robbery of a clothing store seven years ago.
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